The present invention relates to an apparatus for separation/enrichment of isotopes of a uniform compound, and to an apparatus and method for obtaining heavy oxygen water in which the oxygen isotopes 17O and 18O (referred to as heavy oxygen isotopes) within the water molecules have been enriched. More specifically, the present invention relates to a method of producing water enriched in the oxygen isotopes of 17O and 18O in which oxygen is enriched in 16O17O, 16O18O, 17O17O, 17O18O, and 18O18O by cryogenic distillation of oxygen, and then converted to water, and to a method of producing water which is further enriched in the oxygen isotopes of 17O and 18O in which oxygen is enriched in 16O17O, 16O18O, 17O17O, 17O18O, and 18O18O by cryogenic distillation of oxygen, and then converted to water which is then subject to water distillation.